Welding methods

ABSTRACT

A visually seamless method of joining a first piece of metal and a second piece of metal is described. The first piece of metal is placed in contact with an edge of the second piece of metal. In some embodiments, the edge includes a sacrificial lip. The first piece of metal forming a junction area with the edge of the second piece of metal, applying a forging force to the first piece of metal, the forging force having an effect of creating an extremely tight fit up between the first and the second pieces of metal, welding the first and the second pieces to form an assembly and forming a cosmetically enhancing protective layer on the surface of the assembly, the protective layer obscuring any visible artifacts on the surface of the assembly, the obscured visible artifacts including any discoloration or discontinuity created by the laser welding.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 13/615,516filed Sep. 13, 2012 entitled “LASER WELDING APPARATUS,” which is acontinuation of U.S. patent application Ser. No. 12/571,122, filed Sep.30, 2009, now U.S. Pat. No. 8,338,737 issued Dec. 25, 2012, entitled“COMPUTER HOUSING,” which are incorporated herein by reference for allpurposes.

This application is also related to commonly-owned U.S. patentapplication Ser. No. 12/570,972, now U.S. Pat. No. 7,965,498 issued Jun.21, 2011 entitled, “COVER GLASS TO HOUSING INTERFACE SYSTEM,” which isincorporated herein by reference for all purposes.

FIELD

This application relates generally to improving the aesthetic look andfeel of products formed by welding at least two pieces of metaltogether. Such products can include, for example, furniture,automobiles, and housings suitable for accommodating electronic devicessuch as computers and consumer electronics. In particular, thisapplication describes welding operations that create visually seamlesswelds.

BACKGROUND

The art of joining at least two metal pieces together includes suchprocesses as welding in its many forms. However, most applicationswhereby separate pieces of metal are joined are focused more on thestrength of the bond and less on the appearance of the bond. If,however, the appearance of the bond is important, it will often beprecisely welded and then painted (such as a bicycle frame), orprecisely welded, ground down, and then painted (such as a car frame).Currently, there is trend in consumer electronic products (such ascomputers and hand held devices) to use materials that are both strong,resilient and aesthetically pleasing. One such material is aluminum thathas the ability to be formed into any number of suitable shapes,anodized to provide a protective coat that is also pleasing to the eye,and provide an overall aesthetically pleasing experience to the user.

However, when using aluminum to create enclosures, such as a housing fora computer assembly, several separate pieces of aluminum must be joinedtogether. Some of these joined pieces are clearly visible to a user ofthe computer. Any visible artifact (such as a noticeable seam, variationin color, variation in surface texture) can distract from the overallaesthetic appearance of the consumer product. Clearly these visibleartifacts are not acceptable when a computer manufacturer places a highvalue on both the strength of the bond and the appearance of thehousing.

Although the prior art effectively discloses any number of techniquesfor joining together at least two metal pieces, there is still a needfor a metal joining technique that provides a strong as well asapparently seamless metal joint.

SUMMARY

This application describes a number of embodiments that relate tosystems, methods, and apparatus for creating an apparently seamlessjoint between two metal pieces. In particular, the embodiments relate tovarious techniques for forming apparently seamless joints in a metalsuch as those used to create a housing formed of, for example, aluminumsuitable for enclosing and supporting electronic components.

A method of joining a first piece of metal and a second piece of metalis described. The method can be carried out by performing at least thefollowing operations. Placing the first piece of metal in contact withan edge of the second piece of metal. In some embodiments the edge ofthe second piece of metal includes a sacrificial lip. In any case, theedge of the second piece of metal and the first piece of metal forming ajunction area, applying a forging force to the first piece of metal, theforging force having an effect of creating an extremely tight fit upbetween the first and the second pieces of metal at the junction area,forming an assembly by welding the junction area to form a weld, theweld being essentially invisible to an observer, the assembly includingthe joined first and second pieces of metal, and forming a cosmeticallyenhancing protective layer on the surface of the assembly, theprotective layer obscuring any visible artifacts on the surface of theassembly.

In one aspect, the first piece of metal can take the form of a metal barand the second piece of metal can take the form of a metal housing eachbeing formed of aluminum joined to form a computer housing. Theprotective layer can be formed by anodizing the surfaces of the computerhousing and the welding can be laser welding.

A computer housing is disclosed. The computer housing formed by at leasta metal frame and a metal bar joined together at an essentiallyinvisible laser weld joint. The essentially invisible weld formed byfixturing the metal frame and placing the metal bar onto the fixturedmetal frame of the metal bar and the metal frame forming a junctionregion, applying a forging force onto the metal bar that causes at leasta portion of the metal bar in contact with the metal housing at thejunction region to physically deform in relation to the metal frame,forming the computer housing by welding the junction region, and forminga protective layer on the computer housing, the protective layer hidingfrom view surface defects caused by the welding.

A method of laser welding a first and a second piece of metal togetherin a small enclosed area is described. The method can be carried out bycarrying out at least the following operations. Providing the laserwelding apparatus, the laser welding apparatus having at least aprotective cover glass, in the absence of a cross jet flow, providing anatmosphere of inert gas in the vicinity of a laser target, and firingthe laser at the laser target, wherein the absence of the cross jet flowpreserves the inert atmosphere of inert gas in the vicinity of the lasertarget thereby substantially reducing an amount of laser caused debrisfrom reaching the cover glass, thereby extending a useful life of thecover glass.

Computer readable medium for encoding computer program code executableby a processor, the processor controlling a manufacturing operation forjoining a first piece of metal and a second piece of metal is disclosed.The computer readable medium including at least computer code forplacing the first piece of metal in contact with an edge of the secondpiece of metal forming a junction area, computer code for applying aforging force to the first piece of metal, the forging force having aneffect of creating an extremely tight fit up between the first and thesecond pieces of metal, computer code for forming an assembly by weldingthe junction area to form a weld, the weld being essentially invisibleto an observer, the assembly including the joined first and secondpieces of metal, and computer code for forming a cosmetically enhancingprotective layer on the surface of the assembly, the protective layerobscuring any visible artifacts on the surface of the assembly, theobscured visible artifacts including any discoloration or discontinuitycreated by the welding.

Other aspects and advantages of the invention will become apparent fromthe following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 shows a front view of a finished housing suitable for enclosingand supporting a computer/display assembly in accordance with thedescribed embodiments.

FIG. 2A shows a front view of an initial stage in the fabrication ofhousing in accordance with the described embodiments.

FIGS. 2B and 2C show representative embodiments of a baffle system.

FIG. 3 shows a representative bar pocket used to align a metal bar to ametal frame in accordance with the described embodiments.

FIG. 4 shows a side perspective view of assembly secured within fixturein accordance with the described embodiments.

FIG. 5 shows a close up cut away view of a portion of junction areashown in FIG. 4 at a line A-A.

FIG. 6 shows representative keyhole weld having weld nugget that formsthe actual weld in accordance with the described embodiments.

FIGS. 7 and 8 show results of representative finishing operations inaccordance with the described embodiments.

FIGS. 9A-9B show representative laser welding assembly in accordancewith the described embodiments.

FIG. 10 shows a flowchart detailing process for joining at least twopieces of metal by a weld that can be essentially invisible to anobserver.

DETAILED DESCRIPTION

Reference will now be made in detail to selected embodiments an exampleof which is illustrated in the accompanying drawings. It should beunderstood that the described embodiments are not intended to be limitedto one preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of defined by the appended claims.

The disclosed embodiments relate to seamlessly joining at least twopieces of metal together. In one embodiment, the joined pieces of metalcan form part of a computer housing. The computer housing being suitablefor enclosing and supporting a computer/display assembly and formed ofaluminum. The computer housing can be formed of at least two aluminumparts that can include at least a first and a second piece of metal. Thefirst and second pieces of metal can take the form of a housing body anda metal bar. Prior to the metal bar and the housing body being joined, abaffle formed of substantially the same material as the housing body canbe spot welded to an inside surface of the housing body. The baffle canbe configured to substantially cover an opening in the housing body. Thebaffle can be used to obscure a view through the opening from theexternal environment of a computer assembly enclosed within the computerhousing. The baffle can also help to deflect from around the opening anyforces or loads applied to the housing body.

The housing body and the metal bar can be welded together using whatappears to an observer to be a seamless weld joint. By seamless weldjoint, it is meant that to the observer, there is no apparent joint orother discontinuity between the housing body and the metal bar. In thisway, the joined pieces of metal appear to be single and unified. Thefirst and the second pieces of metal can be laser welded together byapplying a forging force to the metal bar in relation to the housingbody. The forging force can mechanically deform the metal bar withrespect to the housing body. The forging force can also cause at leastsome diffusion bonding to occur between the metal bar and the portion ofthe body in contact with the metal bar. The forging force and subsequentdeformation of the metal bar to the housing body can have the effect ofproviding an extremely tight fit up between the metal bar and housingbody.

It should be noted that there are at least two types of lasers that canbe used for welding operation: gas, such as CO₂ and solid state laserboth of which can operate in the infrared region of the electromagneticradiation spectrum that is invisible to the human eye. The solid statelaser can include lasers having a gain medium formed of glass doped withoptically active ions such as neodymium (Nd) or ytterbium (Yb) that canprovide its primary light output in the near-infrared at a wavelength of1.06 microns at laser energies up to about 8000 watts. Laser energy fromsolid state lasers having a wavelength of 1.06 microns can be readilyabsorbed by conductive materials, such as metals, that can typicallyhave a typical reflectance of about 20 to 30 percent. Moreover, thewavelengths represented by 1.06 microns can permit the use of standardoptics to achieve focused spot sizes as small as 0.001″ in diameter. Inthis way, solid-state lasers can be more precise (due to higher qualityoptics) and more versatile due to beam delivery than gas lasers. Forexample, a “throttled down” solid state laser can be used to tack weldthe baffle (and associated L bracket) to the housing body.

In order to join two pieces of metal, laser welding creates what isreferred to as a “keyhole”. The term “keyhole” is a descriptive termthat refers to the plasma and vapor filled keyhole shaped volume formedwhen a high intensity laser beam impinges on the surface of most metals.This keyhole is then traversed through the joint area leaving a (high)aspect ratio weld of solidified material. A fully developed keyhole cantrap almost all of the incident laser power and convert it into heat.Some of the light is absorbed by the vapor, while the rest bouncesaround inside the channel and delivers energy with each reflectioncreating a molten mass that can cool to form what is referred to as theweld nugget, or simply nugget. The keyhole allows lasers to producewelds that are deep and narrow, because power is delivered to theworkpiece through the vapor channel. The aspect ratio (depth/width) ofkeyhole laser welds can be as high as 8:1 but in this case, is closer to1:1.125.

Due to the aspect ratio inherent with keyholing, the portion of the bodyplaced in contact with the metal bar can include a sacrificial lip ofaluminum. The sacrificial lip, although substantially straight wheninitially formed, can become somewhat curved as a result of the appliedforging force. In this way, the sacrificial lip can have an additionalcross-section width of about 10% to about 50% of the original width ofthe housing body. A substantial portion of the nugget can then be formedto include a substantial portion of the sacrificial lip. As the laserbeam moves along the target area (including the sacrificial lip), themolten metal fills in behind the keyhole and solidifies to form theweld. In this way, the sacrificial lip can greatly reduce thepossibility that any post weld finishing operations expose the metalleft behind in the keyhole. After the welding is completed, a protectiveand cosmetic layer can be formed on at least a portion of the housing inthe vicinity of the weld. This protective layer can be an aluminum oxidelayer formed during an anodizing process. In particular embodiments, asurface cleaning operation using abrasive material can be carried outprior to the anodizing whereas in other embodiments an ultrasoniccleaner can be used that removes contaminants via “cavitation”. Thecleaning operation both cleans the surface of contaminants and such butalso helps to obscure any visible artifacts, such as discoloring.

Another aspect of the described embodiments relates to the laser weldingapparatus used to laser weld the body and the metal bar. The laser weldassembly includes a laser configured to provide laser energy to theworkpiece. The laser includes a protective cover glass used to protectthe laser from metallic vapor or liquid metal generated by the laserwelding process. For those applications where the welding optics are inclose proximity to a weld bead, a cross jet provides a jet of highpressure gas that is used to deflect any oncoming metal generated by thelasing of the workpiece from landing on the cover glass or the laseroptics. Any such contamination on the cover glass can adversely affectthe laser welding operation due to, for example, reducing the amount oflaser energy that can be delivered to the workpiece. However, it hasbeen discovered that due to the close proximity of the laser target areaand the laser itself, the flow of high pressure gas from the cross jetnozzle creates a region of relatively lower pressure directly in frontof the laser optics that tends to deplete the inert gas atmosphere inthe target area. This depletion can be caused by bleeding off gas fromthat gas already deposited in the target area in addition to gas bledoff directly from the nozzle(s) supplying the inert gas in the firstplace. The region of relatively lower pressure can also funnel andaccelerate spatter and debris directly from the laser target area to theoptics. Therefore, contrary to convention wisdom, it has been discoveredthat by turning off completely the cross jet flow or not providing thecapability of the cross jet flow in the first place, the low pressurearea is eliminated thereby preserving the inert atmosphere in thevicinity of the laser target resulting in longer than expected usefullifetime of the cover glass.

The embodiments described herein can be illustrated by the figuresEmbodiments are discussed below with reference to FIGS. 1-10. However,those skilled in the art will readily appreciate that the detaileddescription given herein with respect to these figures is forexplanatory purposes and extends beyond these limited embodiments.

FIG. 1 shows a front view of finished housing 100 suitable for enclosingand supporting a computer/display assembly in accordance with thedescribed embodiments. Housing 100 can include rear cover 102 havingregion 104 enclosed by metal frame 106 and supporting rear wall 108.Region 104 can define a volume having a size suitable for accommodatingthe computer/display assembly. The computer/display assembly can besupported by metal frame 106 and protected from the external environmentby rear wall 108. In the disclosed embodiment, rear wall 108 can beformed of rugged material such as plastic or metal such as aluminum ascan metal frame 106. Metal frame 106 can support the computer/displayassembly and a protective cover glass (not shown). Protective coverglass can be configured to cover essentially the entire front facingportion of housing 100 (except for that portion occupied by chin 110). Anumber of protective glass restraint structures 112 attached to metalframe 106 can help keep the protective cover glass from detaching andfalling away from metal frame 106. The aesthetic look and feel of thefinished product can be enhanced using a masking area that can obscurerestraint structures 112 as well as to focus a user's eye on activedisplay area 114. Chin 110 can provide a platform on which protectivecover glass can rest.

Slot shaped opening 116 (also referred to as top vent slot) formed inrear portion 108 (visible in a rear view of housing 100) can be used toprovide a conduit for the exchange of air between enclosure 104 and theexternal environment. This exchange of air can facilitate the cooling ofthe computer/display assembly within enclosure 104. However, in order toprevent a user from actually viewing the computer assembly (and anyother internal components), baffle system 118 can be attached to housing100. Baffle system 118 can also be configured to direct the airflow thatpasses through slot opening 116 from the external environment tospecific areas within enclosure 104. In the described embodiment, bafflesystem 118 can include baffle 120 and L bracket 122. Baffle system 118can be attached to housing 100 by, for example, tack welding one portionof baffle 120 to an interior surface of enclosure 104 and anotherportion to L bracket 122. L bracket 122, in turn, can be attached to theinterior surface of enclosure 104. (FIGS. 2A and 2B show representativeembodiments of baffle system 118).

One drawback to forming slot opening 116 in rear wall 108 is that theremoval of material to form slot opening 116 can result in a localizedarea of a reduced structural integrity simply due to the fact that avoid has been opened in an otherwise continuous rear wall 108. This voidcan result in mechanical deformation of rear wall 108 in proximity toslot opening 116 (referred to as slot misalignment). Slot misalignmentcan result when a force applied to housing 110 causes one side of slotopening 116 to displace relative to the other side of slot opening 116(resembling an overbite or in some cases an underbite). In addition todetracting from the overall appearance of housing 100, such mechanicaldeformation of rear wall 108 can seriously affect dimensional andstructural integrity of housing 100.

However, baffle system 118 can essentially eliminate any stress relatedmechanical deformations of rear wall 108 in the vicinity of slot 116 bydeflecting any force applied to housing 100 effectively bypassing slotopening 116. For example, if a force is applied to a lower portion ofhousing 100, the force will be transmitted through rear wall 108 to andthrough baffle 120 to L bracket 122 and ultimately to that portion ofhousing 100 joined to L bracket 122 bypassing slot opening 116. In thisway, slot opening 116 can be formed prior to operations that requirethat a restraining force be applied to housing 100. Such operations caninclude, for example, laser welding and CNC machining. In this way,substantial savings in both fabrication time and expense can be realizedsince slot opening 116 can be formed in the same set up as thefabrication of rear wall 108.

FIGS. 2-10 illustrate a number of embodiments used in the fabrication ofhousing 100. More particularly, the joining of metal frame 106 andrectangular metal bar 202 to form apparently seamless joining of chin110 and frame 106. For the remainder of this discussion, the metal usedto form rectangular metal bar 202 is aluminum and will hereinafter bereferred to as bar 202.

FIG. 2A shows a front view of an initial stage in the fabrication ofhousing 100 showing assembly 200 with bar 202 secured to metal frame 106(note that the obscured portion of metal frame 106 is shown in dottedlines). In the following discussion, bar 202 can be considered to be theprecursor component of chin 110 shown in FIG. 1. In order to accommodatepost weld finishing operations, bar 202 can have length L+2 d and widthW+w. The post weld finishing operations can be carried out using CNCmachining techniques in order to provide an aesthetically pleasing lookand feel to finished housing 100. For example, bar 202 can have itslength reduced by about at least amount “d” on both sides and its widthreduced by about least amount “w”. In order to assure that bar 202 doesnot move once it is put into place on frame 106, bar 202 can be securedto metal frame 106. Bar 202 can be secured to metal frame 106 using, forexample, laser tack welds at various locations at the interior junctionof bar 202 and frame 106. Since the laser tack welds are only intendedto keep bar 202 from moving, the laser tack welds can be formed using athrottled back solid state laser.

It should be noted that frame 106 can accommodate bar 202 by way of arecess portion referred to as a bar pocket shown in some detail in FIG.3. Bar pocket can be used to align bar 202 in relation to metal frame106. Once bar 202 is in place within the bar pocket, the combination ofbar 202 and metal frame 106 (taken together can be referred to asassembly 200 discussed below) can be secured into a fixture forsubsequent processing.

FIG. 4 shows a side perspective view of assembly 200 secured withinfixture 300. Fixture 300 can secure assembly 200 using a clampingmechanism acting on metal frame 106. Moreover, rear portion 108 can besupported by a “nest” portion of fixture 300 (not shown). In this way,fixture 300 can provide support for assembly 200 during a subsequentlaser welding operation. Once assembly 200 is secured by fixture 300,bar 202 can be secured to metal frame 106. In the described embodiment,the securing can be accomplished by, for example, laser tack welding ata junction of bar 202 and metal frame 106. In this way, once bar 202 issecurely in place, assembly 200 can be placed in an appropriateorientation for subsequent processing. For example, laser welding bar202 to metal frame 106 requires that a forging force be applied to bar202 at a position and direction such that bar 202 deforms in relation tometal frame 106. This forging force can be applied by way of a pressingplate (not shown) that can be formed of tool steel or other appropriatematerial. Therefore, a most appropriate orientation for bar 202 is inthe “face up” direction (or +Z direction) in order that the pressingplate generate sufficient downwardly applied force (i.e., −Z direction)to deform bar 202 onto metal frame 106. In some cases, at least somediffusion bonding between bar 202 and metal frame 106 can occur.Although not of a sufficient degree to forego laser welding, anydiffusion bonding that does occur can enhance the bond created by laserwelding. Other arrangements are possible depending, of course, on theparticular set up to be used, equipment, etc.

In order to more clearly demonstrate the details of the fabricationoperation, FIG. 5 shows a close up cut away view of a portion ofjunction area 400 shown in FIG. 4 at a line A-A. As shown, bar 202 canextend along the X axis distance “d” from exterior wall 402 of housing106 in order to accommodate post weld finishing operations withoutexposing the weld nugget (referred to as blow-through). For example,post weld finishing operations can include removing portion δ of metalframe 106 (in addition to a portion corresponding to distance d of bar202) exposing a new, finished surface corresponding to, for example,dotted line 404. Removal of this material can assist in producing anapparently seamless joint between metal frame 106 and bar 202 whenviewed by an outside observer. However, due to the high aspect ratio ofa keyhole weld nugget created during the laser weld operation,sacrificial portion 406 can be used to prevent any artifacts related tothe weld nugget formed during the laser welding operation from beingexposed on the finished surface.

FIG. 6 shows representative keyhole weld 500 having weld nugget 502 thatforms the actual weld. Weld nugget 502 can be formed of cooled metalthat had been liquefied/vaporized by the laser as the laser energybounced around within the keyhole cavity formed in region targeted bythe laser. In order to prevent exposing weld nugget 502 duringsubsequent machining operations, the laser target area includessacrificial portion 406 having dimensions that can be on the order ofabout 10% to about 50% thickness as metal frame 106. Keyhole weld 500can have a high aspect ratio (at least in the range of 1.1 to about1.125) and as a result weld nugget 502 can extend a distance x into thesurface of the junction of metal frame 106 and bar 202. Depending uponthe desired location of the finished surface (i.e., the value of δ) itis important that substantially none of weld nugget 502 be exposed.Therefore, by having the laser include sacrificial portion 406 in itstarget area, it can be expected that the probability of exposing weldnugget 502 during subsequent finishing operations can be low enough tobe within an acceptable range of probability. Once the bar 202 and metalframe 106 have been welded together, assembly 200 can be removed fromfixture 300 and any of a number of post welding finishing operations canbe performed. These finishing operations can include, for example, usingCNC machining techniques to shape housing 100 into a form suitable forenclosing the computer/display assembly and/or placing the protectiveglass.

FIGS. 7 and 8 show results of representative finishing operations inaccordance with the described embodiments. For example, FIG. 7illustrates a process of removing selected portions of bar 202 to formchin 110. Moreover, in order to accommodate the protective glass layer,selected portions of frame 106 can be removed. In this way, as shown inFIG. 8, chin 110 can act as a shelf onto which the protective glasslayer can rest supported by glass restraints 112 appropriately locatedon metal frame 106. Other finishing operations can include forming aprotective layer on the surface of housing 100 after the mechanicalfinishing operations have been completed. The protective layer can be anoxide layer that can improve its appearance, durability, wear andcorrosion resistance. In addition, the oxide layer can obscure anyremaining visible weld artifacts on the surface of the housing. If themetal is aluminum other suitable material, this protective and cosmeticlayer can be formed during an anodizing process.

FIG. 9A shows a portion of representative laser welding assembly 900 inaccordance with the described embodiments. Generally speaking, the laserand the shield gas go through the same housing. The laser then goesthrough the cover glass and the shield gas is channeled around it beforeboth are shot through a nozzle that guides the shield gas to the weldinglocation and protects the shield gas from spatter. In the particularembodiment shown in FIG. 9A, laser welding assembly 900 includes coverglass holder 904. Laser beam 906 can be directed to desired target area908. Cover glass 910 provides a protective shield from any debrisgenerated by the welding process. In order to prevent unwanted reactions(such as oxidation, or other chemical reactions) from occurring intarget area 908, shield gas can be directed by nozzle 912 to provideatmosphere 914 of inert gas (such as Ar) in target area 908. However,since laser welding assembly 900 must be operate within the closeconfines of bar 202 and body 106, laser welding assembly 900 andtherefore cover glass 910 must also be placed in close proximity totarget area 908 thereby substantially increasing the likelihood ofdebris 916 (also referred to as dross or blowback or spatter) blowingback onto cover glass 910 resulting in reduced laser energy supplied totarget area 908 (and subsequently reducing the quality of the welditself). Conventional thought has it that cross jet 918 that can providecross jet flow 920 (usually of high pressure compressed air) willdeflect debris from target area 908 and in the process reduce the amountof impurities deposited on cover glass 908.

Unfortunately, during the actual laser welding operation it was foundthat the lifetime of cover glass 910 was substantially reduced over thatwhich would be expected even with the deflection caused by cross jetflow 920. It was discovered, however, that high pressure cross jet flow920 was apparently creating region L of relatively low pressure nearnozzle 912. This region of low pressure had the effect of drawing offsome of the inert gas provided by nozzle(s) 912 to target area 908 aswell as directly from nozzle 912. This reduction in inert gas atmosphereand creation of a low pressure region had the effect of generating agreater amount of spatter, funneling said spatter directly at coverglass 910 at an increased rate of speed, and creating an inconsistentweld nugget. In other words, cross jet flow 920 meant to preserve thelifetime of cover glass 910 actually had the opposite effect and createdan unstable welding process overall. Therefore, contrary to conventionalwisdom, turning off cross jet flow 920 (and removing cross jet 918) asshown in FIG. 9B improved the lifetime of cover glass 910 by eliminatingthe region of low pressure that, in turn, returned the inert atmospherein target area 908 to appropriate levels.

FIG. 10 shows a flowchart detailing process 1000 for joining a firstpiece of metal and a second piece of metal by an apparently seamlessweld that can be essentially invisible to an observer. Process 1000 canbegin at 1002 by securing a first piece of metal. In the context of acomputer housing, the first piece of metal can take the form of ahousing having a metal frame and a rear portion each secured within afixture. The second piece of metal can take the form of a metal bar. Inthe described process, the metal frame can be formed of aluminum and beused to support a computer/display assembly whereas the rear portion canenclose a volume suitable for accommodating and protecting thecomputer/display assembly from the external environment. In thedescribed process, the securing can include clamping the metal frame bythe fixture and nesting the rear portion in a nest portion of thefixture. Next at 1004, a second piece of metal (that can take the formof the metal bar) can be placed in contact with the first piece of metal(that can take the form of the housing) and secured in place. In thedescribed embodiment, the metal bar can be placed on and secured to afront portion of the metal frame. The securing can be accomplished bytack welding the metal bar to the metal frame or using small mechanicalclamps. Next at 1006, a full clamping force (also referred to as forgingforce) can be applied to the second metal piece. The forging force cancause the second metal piece to physically deform in relation to thefirst metal piece. Primarily, the forging force can produce a tight fitup between the metal bar and the metal frame. Secondarily, the forgingforce can cause at least some diffusion bonding to occur between themetal bar and the metal frame.

At 1008, a laser weld can be formed at an interior junction area of themetal bar and the metal frame. A sacrificial lip in the junction regioncan be used as a target for the laser. In this way, the weld nuggetformed by the laser is sufficiently removed from an opposite wall of themetal frame to essentially eliminate the possibility of exposing theweld nugget during any post weld finishing operations. At 1010, theassembly formed of the joined first and second metal pieces is removedfrom the fixture and at 1012 structural finishing operations areperformed. The structural finishing operations can include machiningoperations such as CNC machining operations used to bring the exteriordimensions of the assembly to within a specified range of values. Themachining operations can also be used to provide features such as aledge used to support a display protective glass layer. At 1014, anannealing is performed to relieve any stress related defects. At 1016,applying protective layer. The hiding can be accomplished by, forexample, texturing the surface using a cleaning operation such asabrasive blasting. Abrasive blasting can prepare a surface by forciblypropelling a stream of abrasive material against it under high pressurethereby making the surface smoother, remove surface contaminants or insome cases to roughen the surface. Once the surface has been properlyprepared, the surface can be anodized in order to improve itsappearance, durability, wear and corrosion resistance. In addition, theoxide layer formed can obscure any remaining visible weld artifacts onthe surface of the housing. It should be noted that the anodizingprocess was optimized to hide the seam as much as possible and reduceany color variation between the two parts.

The various aspects, embodiments, implementations or features of theinvention can be used separately or in any combination. The inventioncan be implemented by software, hardware or a combination of hardwareand software. The invention can also be embodied as computer readablecode on a computer readable medium for controlling a laser weldingapparatus. The invention can be embodied as computer readable code on acomputer readable medium for controlling a manufacturing line used tofabricate housings. The computer readable medium is any data storagedevice that can store data which can thereafter be read by a computersystem. Examples of the computer readable medium include read-onlymemory, random-access memory, CD-ROMs, DVDs, magnetic tape, optical datastorage devices, and carrier waves. The computer readable medium canalso be distributed over network-coupled computer systems so that thecomputer readable code is stored and executed in a distributed fashion.

The advantages of the invention are numerous. Different aspects,embodiments or implementations may yield one or more of the followingadvantages. One advantage of the invention is that an apparentlyseamless joint can be formed between at least two metallic work pieces.The apparent seamless joint can enhance an overall look and feel of aconsumer product such as a computer housing. The many features andadvantages of the present invention are apparent from the writtendescription and, thus, it is intended by the appended claims to coverall such features and advantages of the invention. Further, sincenumerous modifications and changes will readily occur to those skilledin the art, the invention should not be limited to the exactconstruction and operation as illustrated and described. Hence, allsuitable modifications and equivalents may be resorted to as fallingwithin the scope of the invention.

What is claimed is:
 1. A method of joining a first part and a secondpart, the method comprising: forming a diffusion bond at a junctionregion of the first part and the second part, wherein forming thediffusion bond includes applying a force to the second part such thatthe second part is pressed against the first part; forming an assemblyby welding the first part to the second part, the welding includingdirecting a laser beam at a target area of the junction region, whereinthe welding forms a weld portion at an interior surface of the assembly;and forming a cosmetic layer on an exterior surface, thereby obscuring adefect associated with the weld portion.
 2. The method of claim 1,wherein forming the diffusion bond includes pressing a second surface ofthe second part against a first surface of the first part.
 3. The methodof claim 1, wherein forming the cosmetic layer comprises: forming analuminum oxide layer on the exterior surface.
 4. The method of claim 3,wherein forming the aluminum oxide layer comprises: anodizing theexterior surface.
 5. The method of claim 1, further comprising: prior toforming the cosmetic layer, cleaning the exterior surface using anabrasive material.
 6. The method of claim 1, wherein the first part is afirst portion of a housing and the second part is a second portion of ahousing.
 7. The method of claim 6, wherein the housing is configured tohouse components of a computer.
 8. The method of claim 1, furthercomprising: providing an inert gas in the target area during thewelding.
 9. The method of claim 1, wherein the welding includes weldinga sacrificial portion of the first part.
 10. A method of joining a firstpiece and a second piece, the method comprising: securing the firstpiece; forming a diffusion bond at a junction region of the first pieceand the second piece by pressing the second piece against the firstpiece; and welding the first piece and the second piece together,wherein the welding includes directing a laser beam to a target area ofthe junction region.
 11. The method of claim 10, wherein pressing thesecond piece against the first piece and welding the first piece and thesecond piece have an effect of creating a seamless joint between thefirst and second pieces.
 12. The method of claim 10, wherein pressingthe second piece against the first piece comprises applying a forcedirected in a perpendicular direction with respect to a contact surfaceof the first piece.
 13. The method of claim 10, wherein the weldingincludes liquefying material at a weld region of the junction region.14. The method of claim 10, wherein the welding occurs during thepressing of the first piece against the second piece.
 15. A method ofjoining a first piece and a second piece, the method comprising: forminga diffusion bond between the first piece and the second piece, whereinforming the diffusion bond includes applying a force to the second piecesuch that the second piece is pressed against the first piece; formingan assembly by welding the first piece to the second piece, the weldingincluding directing a laser beam at a target area of a junction regionof the first piece and the second piece, wherein the welding forms aweld portion at an interior surface of the assembly; removing a portionof an exterior surface of the assembly, thereby forming a new exteriorsurface; and forming a cosmetic layer on the new exterior surface,thereby obscuring an artifact associated with the weld portion.
 16. Themethod of claim 15, wherein pressing the first piece against the secondpiece causes diffusion bonding between the first and second pieces atthe junction region.
 17. The method of claim 15, wherein forming thecosmetic layer comprises: forming an aluminum oxide layer on the newexterior surface.
 18. The method of claim 15, wherein the artifactincludes at least one of a discoloration, a discontinuity and a seam.19. The method of claim 15, wherein the force is applied in aperpendicular direction with respect to a contact surface of the firstpiece.
 20. The method of claim 15, further comprising: prior to formingthe cosmetic layer, texturing the new exterior surface using an abrasiveblasting.